The invention relates to a potential-free connection of a first line section of a microwave transmission line with a second line section of the microwave transmission line. Potential-free signifies in this instance that there is no electrically conductive connection.
With applications in microwave technology, situations often occur in which an electrical separation between a measuring value recorder, on the one hand, and a measuring value processing system, on the other hand, is required for a measurement. Such an electrical separation, i.e., a potential-free transition between two separate line sections one of which is connected with the measured value recorder and the other of which is connected with the measured value processing system, can be achieved in principle by means of a transformer, an optoelectronic coupler, or with the help of two capacitors, with one of the capacitors provided in the signal line and the other capacitor provided in the reference line. Such constructions do not represent practicable solutions in the microwave frequency range, however. Alternative solutions with a number of capacitors are indeed conceivable, but such arrangements have only a very small transferable bandwidth, and the breakdown voltage for such a system is only a few hundred volts.
The technical problem of the invention is accordingly to provide a potential-free connection of a first line section of a microwave transmission line with a second line section of the microwave transmission line, in connection with which the potential-free connection should ensure a broadband transfer range for the microwave signal with high breakdown voltage at the same time.
The potential-free connection according to the invention, with which the technical problem derived and described above is solved, is characterized in that the first line section of of the microwave transmission line has a first slotted line, the second line section of the microwave transmission line has a second slotted line and the first slotted line and the second slotted line are each arranged on two opposite sides of a dielectric substrate in such a way that the first slotted line and the second slotted line have a strong electromagnetic coupling but have no electrically conductive connection to each other, i.e., no ohmic contact exists between the first slotted line and the second slotted line.
A preferred further development of the potential-free connection according to the invention consists in that the first slotted line and the second slotted line are straight. Furthermore, the first slotted line preferably extends parallel to the second slotted line, and it is particularly preferable for the first slotted line to extend in true alignment with the second slotted line.
According to a preferred further development of the invention, a particularly good electromagnetic coupling between the first slotted line and the second slotted line is achieved without a conductive connection between them if at one of its end areas, the first slotted line overlaps the second slotted line at one of the latter""s end areas. In this connection, it is particularly preferred for the first slotted line and the second slotted line to each be widened in the area where the two overlap.
Impedance is optimally adapted, according to a preferred further development of the invention, in that the first slotted line and the second slotted line are each widened beyond the area where they overlap. In this connection, a particularly preferred further development of the potential-free connection according to the invention has proven to be a sizing in which the first slotted line and the second slotted line are each widened over a length of 5.5 mm and overlap over a length of 4 mm.
The potential-free connection according to the invention can be produced with various thicknesses of the dielectric substrate. A 0.1 to 0.4 mm thickness of the dielectric substrate has proven particularly suitable for the potential-free connection according to the invention; a 0.25 mm thickness of the dielectric substrate is particularly preferred.
With appropriate geometric adaptation of the overlapping slotted lines, dielectric substrates with the widest variety of dielectric constants can be used for the potential-free connection according to the invention. According to a preferred further development of the potential-free connection, a particularly good electromagnetic coupling between the two overlapping slotted lines is obtained when the dielectric constant of the dielectric. substrate is between 1.5 and 5, with a 2.2 dielectric constant of the dielectric substrate being particularly preferred.
For adaptation to an existing circuit arrangement, a construction in which the first line section and/or the second line section each have a transition from the slotted line to a microstrip line has proven to be a particularly preferred further development. In this way, the microwave signal can be fed in or forwarded particularly easily with a coaxial, line through a respective transition from the coaxial line to the microstrip line and vice versa. In this respect, a particularly preferred further development of the potential-free connection according to the invention consists in that at the respective transition from the slotted line to the microstrip line, the slotted line overlaps the microstrip line, the slotted line runs perpendicular to the microstrip line, the microstrip line ends straight shortly after its overlapping with the slotted line, and shortly after its overlapping with the microstrip line, the slotted line ends with a circular recess whose radius corresponds to roughly twice the slot width of the slotted line. In this connection, the slotted line is in the mass surface of the microstrip line, so it has direct contact with the latter line. In this way, a particularly compact transition from the slotted line to the microstrip line is possible.